Malaria is one of the leading causes of death in developing countries, where four strains of malaria parasites have been identified to be infectious to human, which include Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. Plasmodium falciparum is particularly life threatening due to its high morbidity and mortality rate. Pregnant women, infants, and children with compromised immune functions are most vulnerable to infection. To suppress possible pandemic outbreaks of malaria, substantial research efforts have been devoted to early diagnosis and treatment of malaria (EDTM) as the first-line defense against the progression of malaria. These are designed to minimize the spread in endemic regions, and to prevent the transfer of parasites to other countries through tourism. According to the Center for Disease Control (CDC), the onset of flu-like symptoms begins on the ninth to the fourteenth days after infection, and treatment must be administered within twenty-four hours after the start of symptoms. Delay in diagnosis is the major cause of deaths for most infected travelers. Thus, early diagnosis plays the vital role in the surveillance, prevention and treatment of malaria.
Among current approaches in malaria diagnoses, those based on polymerase chain reaction (PCR) provide the highest sensitivity at 0.004 to 5 parasites per μl of blood. However, the most common PCR instruments are not portable and, therefore, inaccessible in most rural regions. Giemsa-stained thick and thin blood films are the most sensitive and specific methods available besides PCR. It exhibits sensitivities between 5 to 20 parasites per μL of blood (0.0001% parasitaemia). However, it requires a carefully prepared sample examined by a specialist, in which malaria infected red blood cells (miRBCs) are identified from 100 to 200 microscopic fields under 1000× magnifications. Traveler's kits, like ICT Malaria Pf/Pv®, Parasight®-F, and OptiMAL®, provide travelers rapid and portable tool to perform self-tests in the field. However, they are limited in sensitivity and specificity and, therefore, inadequate for early-stage malaria detection.
In recent years, advances in cell mechanics research tools have enabled the study of mechanical differences between normal RBCs and miRBCs. Upon infection, human RBCs start to lose their biconcave shape and become more spherical in shape. During the asexual erythrocytic stages of malaria parasite life cycle in the host RBC, the stiffness of the cell body is increased by more than ten times, and knob-like protrusions are formed on the cell surfaces starting at the trophozite stage. These protrusions mediate the cytoadhesion behavior of miRBCs to vascular endothelium, which makes the miRBCs sticky. Similar to human malaria, the avian miRBCs lose their oval shape and form furrow-like structures on cell surfaces similar to human malaria. The cytoadhesion behaviors of miRBCs have been studied with microfluidic devices that mimic the microcirculation environment in living tissues. By culturing vascular endothelium or coating purified receptors in the microfluidic channels, the adhesion probabilities of normal RBCs and miRBCs were almost the same under 20 mPa shear stress. However, normal RBCs rapidly detached from the substrate once the wall shear stress was elevated above this value. At least three mechanical biomarkers could potentially be used to diagnose malaria including: (1) elevated stiffness of the cell body, (2) altered cell morphology, and (3) increased adhesiveness to appropriately treated microchannel surfaces. The present invention addresses the third option of exploiting the increasing adhesiveness of miRBCs to detect malaria infection.